1. Field of the Invention
The present invention relates to methods and apparatus for directing and controlling electromagnetic power. More specifically, the present invention relates to variable power dividers, beamsplitters and etc.
2. Description of the Related Art
For a variety of applications, there is a ongoing need for systems and methods for directing and controlling electromagnetic power at higher power levels and higher frequencies. For example, there is an ongoing need to effect power division at millimeter wave frequencies (30-300 gigahertz) with quasi-optical Gaussian beams carrying more than 100-1000 kilowatts of power. The known prior art in quasi-optical millimeter-wave power division is the wire-grid variable power divider, typically constructed from a closely-spaced array of tightly-stretched parallel wires. Wire grid variable power dividers are common components in many quasi-optical millimeter-wave systems. At low power levels, the heat generated in each wire by the current induced by the incident beam is inconsequential. At sufficiently high power levels, the absorbed heat may cause mechanical failure of the tightly-stretched wires.
For example, the fractional power absorbed by a low-loss wire-grid variable power divider, when aligned to reflect 100% of the incident power, can be as low as 0.001; i.e., for every kilowatt of power carried by the incident beam, the power divider will absorb at least 1 Watt. If the incident beam carries 1 MW, the power divider will absorb at least 1.0 kW, and if the incident beam carries 5 MW, the power divider will absorb at least 5 kW. A wire grid variable power divider may not be able to dissipate this amount of heat, as the ability of the wires comprising the wire grid to dissipate the absorbed power is seriously restricted by their narrow cross section and consequent low thermal conductance.
Hence, a need remains in the art for a system or method for effecting power division in high power, high frequency applications.
The need in the art is addressed by the system and method for effecting variable power division of the present invention. The inventive system includes a conductive plate having a plurality of slots therein. The slots are arranged in a periodic array to transmit, at a first level, electromagnetic waves incident on the plate at a predetermined angle and polarization when the slots are oriented at a first angle relative to an axis of the plate and to reflect, at a second level, the electromagnetic waves incident on the plate; at the predetermined angle when the slots are oriented at a second angle and polarization relative to the axis of the plate. A support mechanism is provided to maintain the plate at a fixed angle relative to the direction of propagation of the incident electromagnetic waves, and means are provided for removing heat absorbed from the incident electromagnetic waves from the edge of the plate.
The invention is adapted for use with an arrangement for rotating the plate from the first orientation angle to the second orientation angle relative to the axis of the plate. In a specific application, the invention is implemented as a variable beamsplitter for use with quasi-optical millimeter-wave beams. The beamsplitter consists of a circular metal plate into which a periodic array of rectangular slots is cut. The plate is arranged so that the incident millimeter-wave beam is incident at an angle of 45xc2x0 relative to the surface of the plate. Furthermore, the polarization of the incident beam is parallel to the surface of the plate. When the orientation of the plate is such that the electric field of the incident beam is perpendicular to the slots (i.e., the electric field is directed across the narrow dimension of the slots), the plate transmits nearly 100% of the incident energy. If the plate is rotated about its axis by 90xc2x0 (while maintaining a 45xc2x0 angle between the incident beam and the plate) so that the incident electric field is parallel to the slots (i.e. the electric field is directed across the wide dimension of the slots), then the plate transmits 0% and reflects nearly 100% of the incident energy at an angle of 90xc2x0 relative to the incident beam. By varying the angle of rotation between 0xc2x0 and 90xc2x0, both the reflected and transmitted power can be varied continuously between 0% and 100% of the incident power.
A novel feature of the invention derives from the use of a slotted plate as a variable beamsplitter for a quasi-optical millimeter-wave beam and its use of the dependence of the reflection and transmission coefficients on the angle between the incident electric field and the axes of the slots, allowing the reflected and transmitted power to be varied continuously by rotating the plate about its axis.